The invention is for methods for producing low-carbon steel from iron ores containing vanadium and/or titanium. The ore is, to a large extent, pre-reduced in a direct reducing plant, and then further processed in a smelting furnace. Finally, the smelted metal, as well as the enriched slag, are tapped and further processed.
The vanadium contained in some iron ores as admixture and/or the vanadium compounds constitute a valuable by-product in the iron production. When processing iron slags containing vanadium, ferro-vanadium may be obtained which is used in steel alloys, for example, or vanadium oxides which are important in the chemical industry, and particularly vanadium pentoxide (V.sub.2 O.sub.5), which is useful as a catalyst in the production of sulfuric acid or dyestuffs.
In the known methods for producing iron by direct reduction, it was impossible, in the processing of iron ores containing titanium or vanadium, to obtain crude iron with higher concentrations of vanadium and/or slag with higher vanadium contents. In known methods for processing iron ores containing titanium or vanadium (Jessop, Medley, Sainsbury: "Steelmaking with New Zealand Iron Sands", Iron and Steel Institute, London, May 1971; Bold, Evans: "Direct Reduction Down Under", Iron and Steel International, June 1977) the ores with the carbon carriers required for the reactions in a revolving tubular oven, as well as for the following reduction in electric furnaces, are fed to a revolving tubular oven with the additions. In this furnace, the volatile components of the carbon compounds are driven out, the ores are heated and the Fe-oxides are partially pre-reduced. The carbonated additions are decomposed in the process.
The entire contents of the revolving tubular oven reach an insulating vat or vessel after pre-reduction, and are charged into an electro reduction furnace while hot. This reduces the iron, as well as the major portion of the vanadium. The crude iron containing vanadium is tapped, and the slag containing the greater portion of the vanadium oxides in low concentration is removed separately. Subsequently, the vanadium in the crude iron is slagged by addition of oxygen in a shaking pan. In order to maintain the carbon content in the crude iron, carbon carriers are added to the shaking pan. The slag containing the V.sub.2 O.sub.5 is removed from the pan while the crude iron is brought to an oxygen blast converter, where it is blasted and becomes steel.
In methods of this kind, the vanadium is bound to a large quantity of crude iron. This permits only the production of crude iron with a low vanadium content. Accordingly, the slag produced by blasting the crude iron is of a relatively low vanadium content.
It is the object of this invention to use the method as initially described to obtain crude iron with much higher vanadium concentrations, as well as slags with much higher vanadium contents. This is solved by a method for producing low carbon steel from iron ores containing vanadium and/or titanium, the steps which comprise selecting said ores containing vanadium and/or titanium, pre-reducing said ores in a pre-reduction oven, the improvement characterized by charging said pre-reduced ores directly into a smelting aggregate together with carbon carriers, said smelting aggregate containing a molten slag layer and lined with a refractory material selected according to the matrix of the molten slag layer, said carbon carriers being only slightly in excess of the stoichiometric quantity required to reduce the iron in said ores, smelting said charged ores into steel, tapping said smelted steel from said smelting aggregate, tapping said slag layer containing vanadium and small quantities of iron oxide from said smelting aggregate, introducing said tapped slag layer into an electric furnace, processing said tapped slag layer in said electric furnace into smelted crude iron high in vanadium content, and transferring said vanadium from said crude iron to a slag rich in vanadium pentoxide under oxidizing conditions.
In the method of this invention, the iron ore containing titanium and/or vanadium is pre-reduced to a large extent and metalized. The material is then introduced into an electro-slag-resistance furnace, contrary to the conventional reduction furnace, for the production of ferro alloys and crude iron. No solid charge column exists above the slag layer in the electro-slag-resistance furnace. The furnace is lined with suitable refractory material, depending upon the matrix of the slag. If the excess carbon amounts to only little above the stoichiometric quantity of the iron to be reduced, the iron is only reduced, not carburized, while the vanadium oxide remains in the matrix slag due to excessive oxygen potential. Only a small portion of the vanadium merges with the steel bath which is tapped, and finished as steel.
The matrix slag containing vanadium, as well as other matrix components and small quantities of iron oxides, is tapped and then further processed in an electro reduction furnace of conventional design. The small quantity of crude iron with increased vanadium content smelted in the reduction furnace is tapped, and either utilized directly as iron-vanadium-alloy, or, for example, further processed in a connected shaking pan by the addition of oxygen into a primary slag with high vanadium content. The remaining small quantity of crude iron, low in vanadium, can be used in other ways. The tapped slag, rich in titanium oxide, if, for example, the basic materials contained a high percentage of Ti-O coming from the reduction furnace, may be further processed.
In a further feature of the invention, the smelted steel from the electro-slag-resistance furnace may be superheated and refined in a properly small electric arc furnace by the addition of steel with a new slag (duplex method). The duplex method is used, advantageously, in those cases where special quality requirements exist for the steel, and where the phosphorus and sulfur values of ores and coal ashes necessitate a base treatment in the steel furnace.
The particular advantages of the method of this invention consist in the fact that the vanadium is bound to a very small quantity of crude iron. This makes it possible to obtain crude iron with a very high concentration of vanadium and to produce, by blasting, a slag with high vanadium content .